Logic between vocabularies is incorrect

Issue Summary

When filtering using multiple categories, the system uses OR logic across vocabularies. For example:

Vocabulary Colors contains Red, Blue
Vocabulary Shapes contains Circle, Square

Say I wanted to only find blue squares. I check "Blue" and "Square", but the system returns all nodes containing "Blue" OR "Square", not "Blue" AND "Square".

This is a critical failure in the search logic, and needs to be fixed.

If this was an intended feature (i.e. you wanted it to behave this way), code an option in so that people can choose AND or OR logic across vocabularies.